Coated cutting tool

ABSTRACT

A coated cutting tool comprising a substrate and a coating layer formed on a surface of the substrate, wherein: the coating layer comprises at least one α-type aluminum oxide layer; and, in the α-type aluminum oxide layer, a texture coefficient TC (0,0,12) of a (0,0,12) plane is from 4.0 or more to 8.4 or less, and a texture coefficient TC (0,1,8) of a (0,1,8) plane is from 0.5 or more to 3.0 or less.

TECHNICAL FIELD

The present invention relates to a coated cutting tool.

BACKGROUND ART

It is well known that a conventional coated cutting tool used for thecutting of, for example, steel or cast iron, is a coated cutting toolwhich is obtained by depositing, via chemical vapor deposition, acoating layer with a total thickness of from 3 μm or more to 20 μm orless on a surface of a substrate consisting of a cemented carbide. Anexample of the coating layer is a coating layer consisting of a singlelayer of one kind selected from the group consisting of a Ti carbide, aTi nitride, a Ti carbonitride, a Ti carboxide, a Ti oxycarbonitride andaluminum oxide, or consisting of multiple layers of two or more kindsselected therefrom.

Patent Document 1 discloses a cutting insert comprising, on a surface ofa substrate, hard coating layers, wherein: at least one of the hardcoating layers is an α-Al₂O₃ layer; in the α-Al₂O₃ layer, a texturecoefficient TC (0012) thereof is 5 or more; the residual stress of theα-Al₂O₃ layer is from 0 MPa or higher to 300 MPa or lower; and theresidual stress of the substrate is from −2,000 MPa or higher to −400MPa or lower.

CITATION LIST Patent Documents

Patent Document 1: JP2014-530112 T

SUMMARY Technical Problem

An increase in speed, feed and depth of cut has become more conspicuousin cutting in recent times. As a result, cracking generated from a toolsurface due to a load applied onto an edge during machining may reachtoward a substrate, or cracking generated from a substrate due to arapid increase/decrease in edge temperature may reach into a coatinglayer. These points often result in tool fracturing.

Based on such background, the tool disclosed in Patent Document 1 abovehas excellent wear resistance but has insufficient fracture resistanceunder cutting conditions which place a large load on a coated cuttingtool, and the life thereof is therefore required to be further improved.

The present invention has been made in order to solve this problem, andan object of the present invention is to provide a coated cutting toolwhich has excellent wear resistance and fracture resistance and whichaccordingly has a long tool life.

Solution to Problem

The present inventors have conducted studies regarding extending thetool life of a coated cutting tool from the above-described perspectiveand have then found that the following configurations, includingoptimizing the crystal orientation of an α-type aluminum oxide layer,allow the fracture resistance to be improved, and found that, as aresult, the tool life of the coated cutting tool can be extended, andthis has led to the completion of the present invention.

Namely, the gist of the present invention is as set forth below:

[1] A coated cutting tool comprising a substrate and a coating layerformed on a surface of the substrate, wherein:

the coating layer comprises at least one α-type aluminum oxide layer;and

in the α-type aluminum oxide layer, a texture coefficient TC (0,0,12) ofa (0,0,12) plane represented by formula (1) below is from 4.0 or more to8.4 or less, and a texture coefficient TC (0,1,8) of a (0,1,8) planerepresented by formula (2) below is from 0.5 or more to 3.0 or less.

$\begin{matrix}{{{TC}( {0,0,12} )} = {\frac{I( {0,0,12} )}{I_{0}( {0,0,12} )}\{ {\frac{1}{9}{\sum\frac{I( {h,k,l} )}{I_{0}( {h,k,l} )}}} \}^{- 1}}} & (1) \\{{{TC}( {0,1,8} )} = {\frac{I( {0,1,8} )}{I_{0}( {0,1,8} )}\{ {\frac{1}{9}{\sum\frac{I( {h,k,l} )}{I_{0}( {h,k,l} )}}} \}^{- 1}}} & (2)\end{matrix}$(In formulae (1) and (2), I (h,k,l) denotes a peak intensity for an(h,k,l) plane in X-ray diffraction of the α-type aluminum oxide layer,I₀ (h,k,l) denotes a standard diffraction intensity for an (h,k,l) planewhich is indicated on JCPDS Card No. 10-0173 for α-type aluminum oxide,and (h,k,l) refers to the nine crystal planes of (0,1,2), (1,0,4),(1,1,0), (1,1,3), (1,1,6), (0,1,8), (2,1,4), (3,0,0) and (0,0,12).)

[2] The coated cutting tool according to [1], wherein, in the α-typealuminum oxide layer, the texture coefficient TC (0,0,12) is from 5.0 ormore to 8.2 or less.

[3] The coated cutting tool according to [1] or [2], wherein, in theα-type aluminum oxide layer, the texture coefficient TC (0,1,8) is from1.0 or more to 2.5 or less.

[4] The coated cutting tool according to any one of [1] to [3], whereina residual stress value in a (1,1,6) plane of the α-type aluminum oxidelayer is, in at least part thereof, from −300 MPa or higher to 300 MPaor lower.

[5] The coated cutting tool according to any one of [1] to [4], whereinan average thickness of the α-type aluminum oxide layer is from 1.0 μmor more to 15.0 μm or less.

[6] The coated cutting tool according to any one of [1] to [5], whereinthe coating layer comprises, between the substrate and the α-typealuminum oxide layer, a Ti compound layer containing a Ti compound of Tiand an element of at least one kind selected from the group consistingof C, N, O and B.

[7] The coated cutting tool according to [6], wherein the Ti compoundlayer comprises at least one TiCN layer, and an average thickness of theTiCN layer is from 2.0 μm or more to 20.0 μm or less.

[8] The coated cutting tool according to any one of [1] to [7], whereinan average thickness of the coating layer is from 3.0 μm or more to 30.0μm or less.

[9] The coated cutting tool according to any one of [1] to [8], whereinthe substrate is a cemented carbide, cermet, ceramic or a cubic boronnitride sintered body.

Advantageous Effects of Invention

The present invention can provide a coated cutting tool which hasexcellent wear resistance and fracture resistance and which accordinglyhas a long tool life.

DESCRIPTION OF EMBODIMENTS

An embodiment for carrying out the present invention (hereinafter simplyreferred to as the “present embodiment”) will hereinafter be describedin detail. However, the present invention is not limited to the presentembodiment below. Various modifications may be made to the presentinvention without departing from the gist of the invention.

The coated cutting tool according to the present embodiment is a coatedcutting tool comprising a substrate and a coating layer formed on asurface of the substrate, wherein: the coating layer comprises at leastone α-type aluminum oxide layer; and, in the α-type aluminum oxidelayer, a texture coefficient TC (0,0,12) of a (0,0,12) plane representedby formula (1) below is from 4.0 or more to 8.4 or less, and a texturecoefficient TC (0,1,8) of a (0,1,8) plane represented by formula (2)below is from 0.5 or more to 3.0 or less.

$\begin{matrix}{{{TC}( {0,0,12} )} = {\frac{I( {0,0,12} )}{I_{0}( {0,0,12} )}\{ {\frac{1}{9}{\sum\frac{I( {h,k,l} )}{I_{0}( {h,k,l} )}}} \}^{- 1}}} & (1) \\{{{TC}( {0,1,8} )} = {\frac{I( {0,1,8} )}{I_{0}( {0,1,8} )}\{ {\frac{1}{9}{\sum\frac{I( {h,k,l} )}{I_{0}( {h,k,l} )}}} \}^{- 1}}} & (2)\end{matrix}$

Herein, in formulae (1) and (2), I (h,k,l) denotes a peak intensity foran (h,k,l) plane in X-ray diffraction of the α-type aluminum oxidelayer, I₀ (h,k,l) denotes a standard diffraction intensity for an(h,k,l) plane which is indicated on JCPDS Card No. 10-0173 for α-typealuminum oxide, and (h,k,l) refers to the nine crystal planes of(0,1,2), (1,0,4), (1,1,0), (1,1,3), (1,1,6), (0,1,8), (2,1,4), (3,0,0)and (0,0,12).

The coated cutting tool of the present embodiment comprises theabove-described configurations, and this allows the wear resistance andfracture resistance of the coated cutting tool to be improved; as aresult, the tool life thereof can be extended. The factors for theimprovements in wear resistance and fracture resistance of the coatedcutting tool of the present embodiment can be considered to be set forthas follows; however, such factors are not limited to those set forthbelow. That is, firstly, in the α-type aluminum oxide layer of thepresent embodiment, the texture coefficient TC (0,0,12) of the (0,0,12)plane represented by formula (1) above is from 4.0 or more to 8.4 orless, and this indicates a high ratio of a peak intensity I (0,0,12) fora (0,0,12) plane, thereby leading to preferential orientation of a(0,0,12) plane. This allows for the suppression of crater wear, therebyresulting in improved wear resistance. Meanwhile, in the α-type aluminumoxide layer of the present embodiment, the texture coefficient TC(0,1,8) of the (0,1,8) plane represented by formula (2) above is from0.5 or more to 3.0 or less, and this indicates a high ratio of a peakintensity I (0,1,8) for a (0,1,8) plane, thereby leading to preferentialorientation of a (0,1,8) plane. This allows for the suppression of thegeneration of cracking, in particular, the suppression of the generationof cracking under cutting conditions which involve a high temperature,thereby resulting in improved fracture resistance. The total of thetexture coefficient TC (0,0,12) and the texture coefficient (0,1,8) is4.5 or more, which is equal to or more than the total of the texturecoefficients of the other crystal planes, thereby leading topreferential orientation of a (0,0,12) plane and a (0,1,8) plane overthe other crystal planes, and accordingly, the above improved wearresistance and fracture resistance can be reliably achieved.

A coated cutting tool according to the present embodiment comprises asubstrate and a coating layer provided on the substrate. Specificexamples of types of the coated cutting tool include an indexablecutting insert for milling or turning, a drill and an end mill.

The substrate in the present embodiment is not particularly limited, aslong as it may be used as a substrate for a coated cutting tool.Examples of the substrate include a cemented carbide, cermet, ceramic, acubic boron nitride sintered body, a diamond sintered body andhigh-speed steel. From among the above examples, the substrate ispreferably comprised of a cemented carbide, cermet, ceramic or a cubicboron nitride sintered body as this provides further excellent wearresistance and fracture resistance, and, the substrate is furtherpreferably comprised of a cemented carbide.

It should be noted that the surface of the substrate may be modified.For instance, when the substrate is comprised of a cemented carbide, aβ-free layer may be formed on the surface thereof, and when thesubstrate is comprised of cermet, a hardened layer may be formed on thesurface thereof. The operation and effects of the present invention arestill provided even if the substrate surface has been modified in thisway.

The average thickness of the coating layer in the present embodiment ispreferably from 3.0 μm or more to 30.0 μm or less. If the averagethickness of the coating layer is 3.0 μm or more, this indicates thetendency of the wear resistance to be further improved, and if theaverage thickness thereof is 30.0 μm or less, this indicates thetendency of the adhesion of the coating layer with the substrate and thefracture resistance to be further increased. From the same perspective,the average thickness of the coating layer is more preferably from 3.0μm or more to 20.0 μm or less, and is further preferably from 5.0 μm ormore to 20.0 μm or less. It should be noted that the average thicknessof each layer in the coated cutting tool of the present embodiment canbe obtained by: measuring the thickness of each layer and the thicknessof the entire coating layer from each of the cross-sectional surfaces atthree or more locations; and calculating the average value of theresulting measurements.

The coating layer in the present embodiment includes at least one α-typealuminum oxide layer. In the α-type aluminum oxide layer, a texturecoefficient TC (0,0,12) of a (0,0,12) plane represented by formula (1)above is from 4.0 or more to 8.4 or less. If the texture coefficient TC(0,0,12) is increased, the ratio of a peak intensity I (0,0,12) for the(0,0,12) plane is high, thereby resulting in improved wear resistance asthis leads to the suppression of crater wear. From the same perspective,the texture coefficient TC (0,0,12) in the α-type aluminum oxide layeris preferably from 5.0 or more to 8.2 or less.

In the α-type aluminum oxide layer, a texture coefficient TC (0,1,8) ofa (0,1,8) plane represented by formula (2) above is from 0.5 or more to3.0 or less. If the texture coefficient TC (0,1,8) is increased, theratio of a peak intensity I (0,1,8) for the (0,1,8) plane is high, as aresult of which the occurrence of cracking can be suppressed, and, inparticular, the occurrence of cracking can be suppressed even undercutting conditions which involve a high temperature, thereby leading toexcellent fracture resistance. From the same perspective, the texturecoefficient TC (0,1,8) in the α-type aluminum oxide layer is preferablyfrom 1.0 or more to 2.5 or less.

The average thickness of the α-type aluminum oxide layer in the presentembodiment is preferably from 1.0 μm or more to 15.0 μm or less. If theaverage thickness of the α-type aluminum oxide layer is 1.0 μm or more,this indicates the tendency of the crater wear resistance in the rakesurface of the coated cutting tool to be further improved. Meanwhile, ifthe average thickness of the α-type aluminum oxide layer is 15.0 μm orless, this indicates the tendency of the fracture resistance to befurther improved as peeling is further suppressed. From the sameperspective, the average thickness of the α-type aluminum oxide layer ismore preferably from 3.0 μm or more to 12.0 μm or less.

As to the peak intensity of each plane index of the α-type aluminumoxide layer, such peak intensity can be measured using a commerciallyavailable X-ray diffractometer. For instance, when performing an X-raydiffraction measurement, with an X-ray diffractometer “RINT TTR III”manufactured by Rigaku Corporation, by means of a 2θ/θ focusing opticalsystem with Cu-Kα radiation under the following conditions: an output:50 kV, 250 mA; an incident-side solar slit: 5°; a divergencelongitudinal slit: 2/3°; a divergence longitudinal limit slit: 5 mm; ascattering slit: 2/3°; a light-receiving side solar slit: 5°; alight-receiving slit: 0.3 mm; a BENT monochromater; a light-receivingmonochrome slit: 0.8 mm; a sampling width: 0.01°; a scan speed: 4°/min;and a 2θ measurement range: 20°-155°. As a result, the peak intensitiesof all the plane indices indicated on JCPDS Card No. 10-0173 can bemeasured. When obtaining the peak intensity of each plane index from anX-ray diffraction pattern, analysis software included with the X-raydiffractometer may be used. With such analysis software, backgroundprocessing and Kα2 peak removal are conducted using cubic spline, andprofile fitting is conducted using Pearson-VII function, whereby eachpeak intensity can be obtained. It should be noted that, when each typeof coating layer is formed so as to be closer to the substrate than theα-type aluminum oxide layer, each peak intensity can be measured by athin-film X-ray diffraction method in order to avoid the influence ofsuch type of coating layer. Further, when each type of coating layer isformed so as to be further outward than the α-type aluminum oxide layer,such type of coating layer may be removed via buffing, and then an X-raydiffraction measurement may be performed.

In the present embodiment, the residual stress value in a (1,1,6) planeof the α-type aluminum oxide layer is preferably, at least in partthereof, from −300 MPa or higher to 300 MPa or lower. If the residualstress value is −300 MPa or higher, this indicates the tendency of thewear resistance to be improved because the progress of wear—which startsfrom the time when particles fall off from the α-type aluminum oxidelayer—can be suppressed. Further, if the residual stress value is 300MPa or lower, this indicates the tendency of the fracture resistance ofthe coated cutting tool to be further improved because the occurrence ofcracking in the α-type aluminum oxide layer can be further suppressed.From the same perspective, the residual stress value in the (1,1,6)plane of the α-type aluminum oxide layer is more preferably from −300MPa or higher to 100 MPa or lower.

Herein, the term “at least in part thereof” indicates that, it is notnecessary to satisfy, in the entire α-type aluminum oxide layer, theabove residual stress value range in the (1,1,6) plane of the α-typealuminum oxide layer, and such term also indicates that it is onlyrequired to satisfy the above residual stress value range in the (1,1,6)plane of the α-type aluminum oxide layer in a specific area such as arake surface.

The residual stress value of the α-type aluminum oxide layer can bemeasured by a sin²φ method using an X-ray stress measuring apparatus.For instance, the residual stresses at any three points included in thecoating layer are measured via the sin²φ method, and the average valueof the residual stresses at such three points is then obtained. Anythree points, serving as measurement locations, in the coating layerare, for example, selected in such a way as to be 0.1 mm or more apartfrom one another.

In order to measure the residual stress value in the (1,1,6) plane ofthe α-type aluminum oxide layer, the (1,1,6) plane of the α-typealuminum oxide layer which serves as a measurement subject is selected.More specifically, a sample in which an α-type aluminum oxide layer isformed is subjected to analysis with an X-ray diffractometer. Then, anexamination is conducted regarding variations in the diffraction angleof the (1,1,6) plane when a change is made to an angle φ formed by asample plane normal and a lattice plane normal.

The coating layer of the present embodiment preferably comprises,between the substrate and the α-type aluminum oxide layer, a Ti compoundlayer containing a Ti compound of Ti and an element of at least one kindselected from the group consisting of C, N, O and B, as this leads tofurther improved wear resistance and adhesion. The Ti compound layer,from the same perspective, preferably contains a Ti compound of Ti andan element of at least one kind selected from the group consisting of C,N and O.

The Ti compound layer of the present embodiment preferably comprises atleast one TiCN layer because this leads to further improved wearresistance. The average thickness of the TiCN layer is preferably from2.0 μm or more to 20.0 μm or less. If the average thickness of the TiCNlayer is 2.0 μm or more, this indicates the tendency of the wearresistance to be further improved, and, if such average thickness is20.0 μm or less, this indicates the tendency of the fracture resistanceto be further improved as peeling is further suppressed. From the sameperspective, the average thickness of the TiCN layer is more preferablyfrom 5.0 μm or more to 15.0 μm or less.

The Ti compound layer of the present embodiment preferably comprises alowermost layer, being comprised of TiN, between the substrate and theTiCN layer as this leads to improved adhesion. The average thickness ofthe lowermost layer is preferably from 0.1 μm or more to 0.5 μm or less.If the average thickness of the lowermost layer is 0.1 μm or more, thelowermost layer has a more uniform structure, thereby leading to thetendency of the adhesion to be further improved. Meanwhile, if theaverage thickness of the lowermost layer is 0.5 μm or less, this furtherprevents the lowermost layer from serving as a starting point forpeeling, thereby leading to the tendency of the fracture resistance tobe further increased.

The coating layer of the present embodiment preferably comprises anoutermost layer, being comprised of TiN, on the opposite side to thesubstrate as this makes it possible to confirm the usage state of thecoated cutting tool, thereby leading to excellent visibility. Theaverage thickness of the outermost layer is preferably from 0.2 μm ormore to 1.0 μm or less. This is preferable in that: if the averagethickness of the outermost layer is 0.2 μm or more, this provides theeffect of further suppressing the falling of particles from the α-typealuminum oxide layer; and, if such average thickness is 1.0 μm or less,this leads to further improved fracture resistance.

The outermost layer and the lowermost layer are each a layer comprisedof TiN. However, each of such layers may contain a very small amount ofcomponents other than TiN, as long as it has the above-describedrelevant configuration and provides the operation and effects of eitherthe outermost layer or the lowermost layer.

The Ti compound layer of the present embodiment preferably comprises,between the TiCN layer and the α-type aluminum oxide layer, anintermediate layer, being comprised of TiCNO or TiCO, as this leads tofurther improved adhesion. The average thickness of such intermediatelayer is preferably from 0.2 μm or more to 1.5 μm or less. This ispreferable in that: if the average thickness of the intermediate layeris 0.2 μm or more, this indicates the tendency of the adhesion to befurther improved; and, if such average thickness is 1.5 μm or less, thisindicates the tendency of the texture coefficient TC (0,1,8) in theα-type aluminum oxide layer to have a greater value.

The intermediate layer is a layer comprised of TiCNO or TiCO. However,such intermediate layer may contain a very small amount of componentsother than the above compounds, as long as it has the aboveconfiguration and provides the operation and effects of the intermediatelayer.

Examples of a method of forming layers that constitute a coating layerin a coated cutting tool according to the present embodiment include themethod set forth below. However, such method of forming layers is notlimited thereto.

For instance, a TiN layer can be formed by chemical vapor depositionwith a raw material gas composition of TiCl₄: from 5.0 mol % or more to10.0 mol % or less, N₂: from 20 mol % or more to 60 mol % or less, andH₂: the balance, a temperature of from 850° C. or higher to 920° C. orlower, and a pressure of from 100 hPa or higher to 400 hPa or lower.

A TiC layer can be formed by chemical vapor deposition with a rawmaterial gas composition of TiCl₄: from 1.5 mol % or more to 3.5 mol %or less, CH₄: from 3.0 mol % or more to 7.0 mol % or less, and H₂: thebalance, a temperature of from 950° C. or higher to 1,050° C. or lower,and a pressure of from 65 hPa or higher to 85 hPa or lower.

A TiCN layer can be formed by chemical vapor deposition with a rawmaterial gas composition of TiCl₄: from 4.0 mol % or more to 18.0 mol %or less, CH₃CN: from 0.5 mol % or more to 3.0 mol % or less, and H₂: thebalance, a temperature of from 840° C. or higher to 890° C. or lower,and a pressure of from 60 hPa or higher to 80 hPa or lower.

A TiCNO layer can be formed by chemical vapor deposition with a rawmaterial gas composition of TiCl₄: from 3.0 mol % or more to 5.0 mol %or less, CO: from 0.4 mol % or more to 1.0 mol % or less, N₂: from 30mol % or more to 40 mol % or less, and H₂: the balance, a temperature offrom 975° C. or higher to 1,025° C. or lower, and a pressure of from 90hPa or higher to 110 hPa or lower.

A TiCO layer can be formed by chemical vapor deposition with a rawmaterial gas composition of TiCl₄: from 0.5 mol % or more to 1.5 mol %or less, CO: from 2.0 mol % or more to 4.0 mol % or less, and H₂: thebalance, a temperature of from 975° C. or higher to 1,025° C. or lower,and a pressure of from 60 hPa or higher to 100 hPa or lower.

In the present embodiment, a coated cutting tool which involves thecontrolled orientation relationship of an α-type aluminum oxide layercan be obtained by, for example, the method set forth below.

Firstly, a lowermost layer (a TiN layer), a TiCN layer or anintermediate layer is formed on a surface of a substrate of a coatedcutting tool. Then, a surface of the TiN layer, the TiCN layer or theintermediate layer is oxidized. Thereafter, two kinds of nuclei ofaluminum oxide are formed thereon, and an α-type aluminum oxide layer isformed in the state in which such nuclei have been formed. Further, anoutermost layer may be formed as appropriate.

The first nucleus of aluminum oxide is formed with a very small amountof CO gas being caused to flow at a low temperature. This leads to theformation of the first nucleus of aluminum oxide at a very slow rate.Further, the first nucleus of aluminum oxide is minute. The time duringwhich the first nucleus of aluminum oxide is formed is preferably from 2minutes or more to 5 minutes or less. Thus, the α-type aluminum oxidelayer is prone to have preferential orientation of a (0,0,12) plane.

Next, the second nucleus of aluminum oxide is formed. The second nucleusof aluminum oxide is formed with a very small amount of CO gas and C₃H₆gas being caused to flow at a high temperature. Further, the secondnucleus of aluminum oxide can be formed within the first nucleus ofaluminum oxide or on the surface thereof. The time during which thesecond nucleus of aluminum oxide is formed is preferably from 2 minutesor more to 5 minutes or less. The combination of this step and anoxidation step allows the α-type aluminum oxide layer to be prone tohave preferential orientation of a (0,1,8) plane.

In order to obtain an α-type aluminum oxide layer which satisfies a TC(0,0,12) and a TC (0,1,8), after the formation of the two kinds ofnuclei of aluminum oxide, the α-type aluminum oxide layer may be formedunder the condition that a CO gas is not caused to flow. At this time,the deposition temperature is preferably made higher than thetemperature at which the first nucleus of aluminum oxide is formed.

More specifically, the oxidation of the surface of the TiN layer, theTiCN layer or the intermediate layer is performed under the conditionsof a raw material gas composition of CO₂: from 0.1 mol % or more to 1.0mol % or less, CO: from 0.1 mol % or more to 0.5 mol % or less, CH₄:from 0.05 mol % or more to 0.2 mol % or less and H₂: the balance, atemperature of from 970° C. or higher to 1,020° C. or lower, and apressure of from 50 hPa or higher to 70 hPa or lower. Here, oxidation ispreferably performed for from 5 minutes or more to 10 minutes or less.

Thereafter, the first nucleus of α-type aluminum oxide is formed bychemical vapor deposition with a raw material gas composition of AlCl₃:from 1.0 mol % or more to 4.0 mol % or less, CO₂: from 1.0 mol % or moreto 3.0 mol % or less, CO: from 0.05 mol % or more to 2.0 mol % or less,HCl: from 2.0 mol % or more to 3.0 mol % or less, and H₂: the balance, atemperature of from 880° C. or higher to 930° C. or lower, and apressure of from 60 hPa or higher to 80 hPa or lower.

Then, the second nucleus of α-type aluminum oxide is formed by chemicalvapor deposition with a raw material gas composition of AlCl₃: from 2.0mol % or more to 5.0 mol % or less, CO₂: from 2.5 mol % or more to 4.0mol % or less, CO: from 1.0 mol % or more to 2.0 mol % or less, HCl:from 2.0 mol % or more to 3.0 mol % or less, C₃H₆: from 0.05 mol % ormore to 0.2 mol % or less, and H₂: the balance, a temperature of from970° C. or higher to 1,030° C. or lower, and a pressure of from 60 hPaor higher to 80 hPa or lower.

Further, the α-type aluminum oxide layer is formed by chemical vapordeposition with a raw material gas composition of AlCl₃: from 2.0 mol %or more to 5.0 mol % or less, CO₂: from 2.5 mol % or more to 4.0 mol %or less, HCl: from 2.0 mol % or more to 3.0 mol % or less, H₂S: from0.15 mol % or more to 0.25 mol % or less, and H₂: the balance, atemperature of from 970° C. or higher to 1,030° C. or lower, and apressure of from 60 hPa or higher to 80 hPa or lower.

As described above, the surface of the TiN layer, the TiCN layer or theintermediate layer is oxidized, and the two kinds of nuclei of aluminumoxide are then formed. Thereafter, an α-type aluminum oxide layer isformed with normal conditions, thereby making it possible to obtain anα-type aluminum oxide layer involving a TC (0,0,12) of 4.0 or more and aTC (0,1,8) of 0.5 or more. At this time, the existence ratio of the twokinds of nuclei of aluminum oxide is adjusted, whereby the orientationrelationship of the α-type aluminum oxide layer can be controlled.

After the formation of the coating layer, dry blasting, wet blasting orshot peening is performed thereon, thereby making it possible to controlthe residual stress value in a (1,1,6) plane of the α-type aluminumoxide layer. For instance, as to the conditions for dry shot blasting, ashot material may be shot onto a surface of the coating layer at a shotvelocity of from 50 m/sec or more to 80 m/sec or less and for a shottime of from 0.5 minutes or more to 3 minutes or less so as to achieve ashot angle of from 30° or more to 70° or less. The medium in dry shotblasting is preferably a material, such as Al₂O₃ or ZrO₂, which has anaverage particle size of from 100 μm or more to 150 μm or less.

The thickness of each layer in the coating layer of the coated cuttingtool of the present embodiment can be measured from a cross-sectionalstructure of the coated cutting tool, using an optical microscope, ascanning electron microscope (SEM), a field emission scanning electronmicroscope (FE-SEM) or the like. It should be noted that the averagethickness of each layer in the coated cutting tool of the presentembodiment may be obtained by: measuring the thickness of each layer atthree or more locations near the position 50 μm from the edge, towardthe center of the rake surface of the coated cutting tool; andcalculating the average value of the resulting measurements. Further,the composition of each layer can be measured from a cross-sectionalstructure of the coated cutting tool of the present embodiment, using anenergy-dispersive X-ray spectroscope (EDS), a wavelength-dispersiveX-ray spectroscope (WDS) or the like.

EXAMPLES

Although the present invention will be described in further detailbelow, with examples, the present invention is not limited to suchexamples.

A cemented carbide cutting insert with a shape of JIS standardCNMA120408 and a composition of 93.0WC-6.4Co-0.6Cr₃C₂ (mass %) wasprepared as a substrate. The cutting edge of such substrate wassubjected to round honing by means of an SiC brush, and the surface ofthe substrate was then washed.

After the substrate surface was washed, a coating layer was formed bychemical vapor deposition. As to invention samples 1 to 11, firstly, thesubstrate was inserted into an external heating chemical vapordeposition apparatus, and a lowermost layer, which is shown in Table 1,was formed on the substrate surface so as to have the average thicknessshown in Table 1. At this time, the lowermost layer was formed under theraw material gas composition, temperature and pressure conditions shownin Table 2. Then, a TiCN layer, which is shown in Table 1, was formed onthe surface of the lowermost layer so as to have the average thicknessshown in Table 1 under the raw material gas composition, temperature andpressure conditions shown in Table 2. Next, an intermediate layer, whichis shown in Table 1, was formed on the surface of the TiCN layer so asto have the average thickness shown in Table 1 under the raw materialgas composition, temperature and pressure conditions shown in Table 2.Thereafter, the surface of the intermediate layer was oxidized for thetime shown in Table 3 and under the raw material gas composition,temperature and pressure conditions shown in Table 3. Then, a firstnucleus of aluminum oxide was formed on the oxidized surface of theintermediate layer under the raw material gas composition, temperatureand pressure conditions shown in Table 4. The time during which thefirst nucleus of aluminum oxide was formed was set at 4 minutes.Further, a second nucleus of aluminum oxide was formed within or on thesurface of the first nucleus of aluminum oxide under the raw materialgas composition, temperature and pressure conditions shown in Table 4.The time during which the second nucleus of aluminum oxide was formedwas set at 4 minutes. Thereafter, an α-type aluminum oxide layer(hereinafter referred to as an α-type Al₂O₃ layer), which is shown inTable 1, was formed on the surface of the intermediate layer and thesurfaces of the two kinds of nuclei of aluminum oxide so as to have theaverage thickness shown in Table 1 under the raw material gascomposition, temperature and pressure conditions shown in Table 5.Lastly, an outermost layer, which is shown in Table 1, was formed on thesurface of the α-type Al₂O₃ layer so as to have the average thicknessshown in Table 1 under the raw material gas composition, temperature andpressure conditions shown in Table 2. As a result, the coated cuttingtools of invention samples 1 to 11 were obtained.

Meanwhile, as to comparative samples 1 to 10, firstly, the substrate wasinserted into an external heating chemical vapor deposition apparatus,and a lowermost layer, which is shown in Table 1, was formed on thesubstrate surface so as to have the average thickness shown in Table 1under the raw material gas composition, temperature and pressureconditions shown in Table 2. Then, a TiCN layer, which is shown in Table1, was formed on the surface of the lowermost layer so as to have theaverage thickness shown in Table 1 under the raw material gascomposition, temperature and pressure conditions shown in Table 2. Next,an intermediate layer, which is shown in Table 1, was formed on thesurface of the TiCN layer so as to have the average thickness shown inTable 1 under the raw material gas composition, temperature and pressureconditions shown in Table 2. Thereafter, the surface of the intermediatelayer was oxidized for the time shown in Table 3 and under the rawmaterial gas composition, temperature and pressure conditions shown inTable 3. Then, one or two kinds of nucleus or nuclei of aluminum oxidewas/were formed on the oxidized surface of the intermediate layer underthe raw material gas composition, temperature and pressure conditionsshown in Table 6. Herein, the term “no step” in Table 6 indicates nostep of forming the second nucleus of aluminum oxide. Further, an α-typeAl₂O₃ layer, which is shown in Table 1, was formed on the surface of theintermediate layer and the surface or surfaces of the nucleus or nucleiof aluminum oxide so as to have the average thickness shown in Table 1under the raw material gas composition, temperature and pressureconditions shown in Table 7. Lastly, an outermost layer, which is shownin Table 1, was formed on the surface of the α-type Al₂O₃ layer so as tohave the average thickness shown in Table 1 under the raw material gascomposition, temperature and pressure conditions shown in Table 2. As aresult, the coated cutting tools of comparative samples 1 to 10 wereobtained.

The thickness of each layer of each of the samples was obtained as setforth below. That is, using an FE-SEM, the average thickness wasobtained by: measuring the thickness of each layer, from each of thecross-sectional surfaces at three locations near the position 50 μm fromthe edge of the coated cutting tool, toward the center of the rakesurface thereof; and calculating the average value of the resultingmeasurements. Using an EDS, the composition of each layer of theobtained sample was measured from the cross-sectional surface near theposition at most 50 μm from the edge of the coated cutting tool, towardthe center of the rake surface thereof.

TABLE 1 Coating layer Lowermost layer TiCN layer Intermediate layerAverage Average Average thickness thickness thickness Sample No.Composition (μm) Composition (μm) Composition (μm) Invention TiN 0.1TiCN 3.4 TiCNO 0.4 sample 1 Invention TiN 0.1 TiCN 6.2 TiCNO 0.4 sample2 Invention TiN 0.3 TiCN 10.0 TiCNO 0.2 sample 3 Invention TiN 0.3 TiCN19.8 TiCNO 0.1 sample 4 Invention TiN 0.5 TiCN 15.4 TiCNO 0.6 sample 5Invention TiN 0.5 TiCN 8.0 TiCNO 0.6 sample 6 Invention TiN 1.2 TiCN 8.2TiCO 0.2 sample 7 Invention TiN 2.0 TiCN 8.2 TiCNO 0.8 sample 8Invention TiC 0.3 TiCN 7.8 TiCNO 0.8 sample 9 Invention TiN 1.0 TiCN 6.0TiCNO 1.0 sample 10 Invention TiN 0.5 TiCN 3.0 TiCO 0.5 sample 11Comparative TiN 0.1 TiCN 3.2 TiCNO 0.4 sample 1 Comparative TiN 0.1 TiCN6.2 TiCNO 0.4 sample 2 Comparative TiN 0.3 TiCN 19.8 TiCNO 0.2 sample 3Comparative TiC 0.3 TiCN 3.0 TiCNO 0.1 sample 4 Comparative TiN 0.5 TiCN8.0 TiCNO 0.2 sample 5 Comparative TiN 0.5 TiCN 15.2 TiCNO 0.2 sample 6Comparative TiN 0.3 TiCN 8.2 TiCNO 0.4 sample 7 Comparative TiN 1.0 TiCN8.2 TiCO 0.6 sample 8 Comparative TiN 1.2 TiCN 8.0 TiCNO 0.6 sample 9Comparative TiN 1.2 TiCN 8.0 TiCNO 1.0 sample 10 Coating layer α-typeAl₂Ol₃ layer Outermost layer Average Average Total Crystal thicknessthickness thickness Sample No. system (μm) Composition (μm) (μm)Invention α 8.0 TiN 0.2 12.1 sample 1 Invention α 8.0 TiN 0.2 14.9sample 2 Invention α 8.2 TiN 0.4 19.1 sample 3 Invention α 8.2 TiN 0.428.8 sample 4 Invention α 5.0 TiN 0.4 21.9 sample 5 Invention α 4.8 TiN0.6 14.5 sample 6 Invention α 10.2 TiN 0.2 20.0 sample 7 Invention α15.2 TiN 0.4 26.6 sample 8 Invention α 2.0 TiN 0.2 11.1 sample 9Invention α 2.2 TiN 0.2 10.4 sample 10 Invention α 3.6 TiN 0.2 7.8sample 11 Comparative α 8.2 TiN 0.2 12.1 sample 1 Comparative α 8.2 TiN0.2 15.1 sample 2 Comparative α 8.0 TiN 0.4 28.7 sample 3 Comparative α4.8 TiN 0.4 8.6 sample 4 Comparative α 5.0 TiN 0.2 13.9 sample 5Comparative α 5.0 TiN 0.2 21.1 sample 6 Comparative α 15.0 TiN 0.6 24.5sample 7 Comparative α 10.2 TiN 0.6 20.6 sample 8 Comparative α 2.0 TiN0.4 12.2 sample 9 Comparative α 7.8 TiN 0.4 18.4 sample 10

TABLE 2 Coating layer Temperature Pressure Raw material composition Type(° C.) (hPa) (mol %) TiN 900 400 TiCl₄: 7.5%, N₂: 40%, H₂: 52.5% TiC1,000 75 TiCl₄: 2.4%, CH₄: 4.6%, H₂: 93.0% TiCN 840 70 TiCl₄: 4.0%,CH₃CN: 0.75%, H₂: 95.25% TiCNO 1,000 100 TiCl₄: 3.5%, CO: 0.7%, N₂:35.5%, H₂: 60.3% TiCO 1,000 80 TiCl₄: 1.3%, CO: 2.7%, H₂: 96.0%

TABLE 3 Temperature Pressure Raw material composition Time Sample No. (°C.) (hPa) (mol %) (min) Invention 990 60 CO₂: 0.4%, CO: 0.2%, CH₄: 0.1%,H₂: 99.3% 6 sample 1 Invention 990 70 CO₂: 0.7%, CO: 0.3%, CH₄: 0.1%,H₂: 98.9% 7 sample 2 Invention 990 70 CO₂: 0.1%, CO: 0.3%, CH₄: 0.1%,H₂: 99.5% 7 sample 3 Invention 1,020 70 CO₂: 0.4%, CO: 0.3%, CH₄: 0.05%,H₂: 99.25% 8 sample 4 Invention 990 60 CO₂: 1.0%, CO: 0.3%, CH₄: 0.1%,H₂: 98.6% 7 sample 5 Invention 970 50 CO₂: 0.7%, CO: 0.1%, CH₄: 0.2%,H₂: 99.0% 7 sample 6 Invention 990 50 CO₂: 0.1%, CO: 0.2%, CH₄: 0.1%,H₂: 99.6% 9 sample 7 Invention 970 60 CO₂: 0.4%, CO: 0.1%, CH₄: 0.2%,H₂: 99.3% 5 sample 8 Invention 990 70 CO₂: 0.4%, CO: 0.3%, CH₄: 0.1%,H₂: 99.2% 8 sample 9 Invention 990 60 CO₂: 0.7%, CO: 0.3%, CH₄: 0.1%,H₂: 98.9% 7 sample 10 Invention 1,020 60 CO₂: 0.4%, CO: 0.4%, CH₄:0.05%, H₂: 99.15% 9 sample 11 Comparative 990 60 CO₂: 0.7%, H₂: 99.3% 6sample 1 Comparative 990 50 CO₂: 0.1%, CH₄: 0.1%, H₂: 99.5% 7 sample 2Comparative 990 60 CO₂: 0.7%, H₂: 99.3% 6 sample 3 Comparative 990 60CO₂: 0.1%, H₂: 99.9% 10 sample 4 Comparative 990 70 CO₂: 0.4%, H₂: 99.6%8 sample 5 Comparative 990 60 CO₂: 0.4%, CO: 0.1%, H₂: 99.3% 5 sample 6Comparative 970 60 CO₂: 0.4%, H₂: 99.6% 9 sample 7 Comparative 990 60CO₂: 0.4%, CO: 0.1%, CH₄: 0.2%, H₂: 99.3% 2 sample 8 Comparative 990 60CO₂: 0.7%, H₂: 99.3% 5 sample 9 Comparative 1,020 60 CO₂: 0.4%, H₂:99.6% 8 sample 10

TABLE 4 Temperature Pressure Raw material composition Sample No. (° C.)(hPa) (mol %) First nucleus formation conditions Invention 900 60 AlCl₃:2.5%, CO₂: 3.0%, CO: 1.0%, HCl: 2.5%, H₂: 91.0% sample 1 Invention 90070 AlCl₃: 4.0%, CO₂: 2.4%, CO: 1.5%, HCl: 2.7%, H₂: 89.4% sample 2Invention 900 70 AlCl₃: 2.2%, CO₂: 1.1%, CO: 1.5%, HCl: 2.0%, H₂: 93.4%sample 3 Invention 930 70 AlCl₃: 3.4%, CO₂: 2.0%, CO: 1.5%, HCl: 3.0%,H₂: 90.1% sample 4 Invention 900 70 AlCl₃: 2.5%, CO₂: 2.5%, CO: 1.5%,HCl: 2.3%, H₂: 91.2% sample 5 Invention 880 70 AlCl₃: 1.8%, CO₂: 2.7%,CO: 0.5%, HCl: 2.5%, H₂: 92.5% sample 6 Invention 900 80 AlCl₃: 3.0%,CO₂: 2.0%, CO: 1.0%, HCl: 2.3%, H₂: 91.7% sample 7 Invention 880 60AlCl₃: 2.5%, CO₂: 3.0%, CO: 0.1%, HCl: 2.5%, H₂: 91.9% sample 8Invention 900 60 AlCl₃: 2.2%, CO₂: 1.1%, CO: 1.5%, HCl: 2.0%, H₂: 93.4%sample 9 Invention 900 70 AlCl₃: 2.5%, CO₂: 2.5%, CO: 1.5%, HCl: 2.3%,H₂: 91.2% sample 10 Invention 930 70 AlCl₃: 1.5%, CO₂: 2.7%, CO: 2.0%,HCl: 2.5%, H₂: 91.3% sample 11 Second nucleus formation conditionsInvention 990 60 AlCl₃: 2.2%, CO₂: 3.4%, CO: 1.3%, HCl: 2.5%, C₃H₆:0.1%, H₂: 90.5% sample 1 Invention 990 70 AlCl₃: 3.6%, CO₂: 4.0%, CO:1.0%, HCl: 2.8%, C₃H₆: 0.1%, H₂: 88.5% sample 2 Invention 990 70 AlCl₃:4.0%, CO₂: 3.0%, CO: 1.7%, HCl: 2.0%, C₃H₆: 0.1%, H₂: 89.2% sample 3Invention 1,030 70 AlCl₃: 2.0%, CO₂: 2.8%, CO: 2.0%, HCl: 2.5%, C₃H₆:0.05%, H₂: 90.65% sample 4 Invention 990 70 AlCl₃: 3.2%, CO₂: 2.5%, CO:1.3%, HCl: 3.0%, C₃H₆: 0.1%, H₂: 89.9% sample 5 Invention 970 70 AlCl₃:4.5%, CO₂: 3.0%, CO: 1.7%, HCl: 2.5%, C₃H₆: 0.2%, H₂: 88.1% sample 6Invention 990 80 AlCl₃: 2.2%, CO₂: 3.4%, CO: 1.7%, HCl: 2.5%, C₃H₆:0.15%, H₂: 90.05% sample 7 Invention 970 60 AlCl₃: 4.5%, CO₂: 3.0%, CO:1.7%, HCl: 2.5%, C₃H₆: 0.2%, H₂: 88.1% sample 8 Invention 990 60 AlCl₃:3.6%, CO₂: 4.0%, CO: 1.0%, HCl: 2.8%, C₃H₆: 0.1%, H₂: 88.5% sample 9Invention 990 70 AlCl₃: 3.6%, CO₂: 4.0%, CO: 1.0%, HCl: 2.8%, C₃H₆:0.1%, H₂: 88.5% sample 10 Invention 1,030 70 AlCl₃: 2.0%, CO₂: 2.8%, CO:2.0%, HCl: 2.5%, C₃H₆: 0.05%, H₂: 90.65% sample 11

TABLE 5 Deposition conditions Temperature Pressure Raw materialcomposition Sample No. (° C.) (hPa) (mol %) Invention 990 60 AlCl₃:3.3%, CO₂: 2.6%, HCl: 2.2%, H₂S: 0.2%, H₂: 91.7% sample 1 Invention 99070 AlCl₃: 3.7%, CO₂: 3.6%, HCl: 2.7%, H₂S: 0.2%, H₂: 90.8% sample 2Invention 990 70 AlCl₃: 3.3%, CO₂: 2.6%, HCl: 2.2%, H₂S: 0.2%, H₂: 91.7%sample 3 Invention 1,030 70 AlCl₃: 4.8%, CO₂: 2.9%, HCl: 2.0%, H₂S:0.15%, H₂: 90.15% sample 4 Invention 990 70 AlCl₃: 3.7%, CO₂: 3.6%, HCl:2.7%, H₂S: 0.2%, H₂: 90.8% sample 5 Invention 970 70 AlCl₃: 2.0%, CO₂:3.6%, HCl: 2.5%, H₂S: 0.25%, H₂: 91.65% sample 6 Invention 990 80 AlCl₃:3.1%, CO₂: 4.0%, HCl: 3.0%, H₂S: 0.2%, H₂: 89.7% sample 7 Invention 97060 AlCl₃: 3.1%, CO₂: 4.0%, HCl: 3.0%, H₂S: 0.2%, H₂: 89.7% sample 8Invention 990 60 AlCl₃: 3.3%, CO₂: 2.6%, HCl: 2.2%, H₂S: 0.2%, H₂: 91.7%sample 9 Invention 990 70 AlCl₃: 3.3%, CO₂: 2.6%, HCl: 2.2%, H₂S: 0.2%,H₂: 91.7% sample 10 Invention 1,030 70 AlCl₃: 2.8%, CO₂: 2.9%, HCl:2.7%, H₂S: 0.15%, H₂: 91.45% sample 11

TABLE 6 Temperature Pressure Raw material composition Sample No. (° C.)(hPa) (mol %) Nucleus formation conditions (1) Comparative 900 60 AlCl₃:2.5%, CO₂: 3.0%, HCl: 2.8%, H₂: 91.7% sample 1 Comparative 900 70 AlCl₃:2.5%, CO₂: 3.0%, HCl: 2.8%, H₂: 91.7% sample 2 Comparative 880 70 AlCl₃:1.8%, CO₂: 2.7%, CO: 0.5%, HCl: 2.5%, H₂: 92.5% sample 3 Comparative1,030 70 AlCl₃: 3.0%, CO₂: 3.4%, HCl: 2.2%, H₂: 91.4% sample 4Comparative 900 70 AlCl₃: 3.0%, CO₂: 3.4%, HCl: 2.2%, H₂: 91.4% sample 5Comparative 880 60 AlCl₃: 2.5%, CO₂: 3.0%, CO: 0.1%, HCl: 2.5%, H₂:91.9% sample 6 Comparative 900 70 AlCl₃: 2.5%, CO₂: 3.0%, HCl: 2.8%, H₂:91.7% sample 7 Comparative 990 60 AlCl₃: 2.5%, CO₂: 3.0%, CO: 0.05%,HCl: 3.5%, H₂: 90.95% sample 8 Comparative 900 60 AlCl₃: 2.5%, CO₂:3.0%, CO: 1.0%, HCl: 2.5%, H₂: 91.0% sample 9 Comparative 900 60 AlCl₃:2.5%, CO₂: 3.0%, CO: 0.05%, HCl: 2.5%, H₂: 91.95% sample 10 Nucleusformation conditions (2) Comparative No step sample 1 Comparative 990 70AlCl₃: 3.6%, CO₂: 4.0%, CO: 1.0%, HCl: 2.8%, C₃H₆: 0.1%, H₂: 88.5%sample 2 Comparative No step sample 3 Comparative No step sample 4Comparative No step sample 5 Comparative 990 70 AlCl₃: 2.5%, CO₂: 3.0%,HCl: 2.5%, H₂: 92.0% sample 6 Comparative No step sample 7 Comparative990 70 AlCl₃: 4.0%, CO₂: 3.0%, CO: 1.7%, HCl: 2.0%, C₃H₆: 0.1%, H₂:89.2% sample 8 Comparative 990 60 AlCl₃: 2.0%, CO₂: 3.5%, HCl: 3.0%, H₂:91.5% sample 9 Comparative 990 70 AlCl₃: 2.5%, CO₂: 3.0%, HCl: 3.5%, H₂:91.0% sample 10

TABLE 7 Deposition conditions Temperature Pressure Raw materialcomposition Sample No. (° C.) (hPa) (mol %) Comparative 990 60 AlCl₃:3.3%, CO₂: 2.6%, HCl: 2.2%, H₂S: 0.2%, H₂: 91.7% sample 1 Comparative990 60 AlCl₃: 3.1%, CO₂: 4.0%, HCl: 3.0%, H₂S: 0.2%, H₂: 89.7% sample 2Comparative 990 70 AlCl₃: 3.3%, CO₂: 2.6%, HCl: 2.2%, H₂S: 0.2%, H₂:91.7% sample 3 Comparative 1,030 70 AlCl₃: 4.8%, CO₂: 2.9%, HCl: 2.0%,H₂S: 0.15%, H₂: 90.15% sample 4 Comparative 990 70 AlCl₃: 3.7%, CO₂:3.6%, HCl: 2.7%, H₂S: 0.2%, H₂: 90.8% sample 5 Comparative 970 70 AlCl₃:2.0%, CO₂: 3.6%, HCl: 2.5%, H₂S: 0.25%, H₂: 91.65% sample 6 Comparative990 80 AlCl₃: 3.1%, CO₂: 4.0%, HCl: 3.0%, H₂S: 0.2%, H₂: 89.7% sample 7Comparative 970 60 AlCl₃: 3.1%, CO₂: 4.0%, HCl: 3.0%, H₂S: 0.2%, H₂:89.7% sample 8 Comparative 990 70 AlCl₃: 3.3%, CO₂: 2.6%, HCl: 2.2%,H₂S: 0.2%, H₂: 91.7% sample 9 Comparative 1,030 70 AlCl₃: 2.8%, CO₂:2.9%, HCl: 2.7%, H₂S: 0.15%, H₂: 91.45% sample 10

As to invention samples 1 to 11 and comparative samples 1 to 10, afterthe formation of the coating layer on the surface of the substrate, dryshot blasting was performed under the shot conditions shown in Table 8,using the shot material shown in Table 8.

TABLE 8 Shot material Shot conditions Average Shot Shot particle sizeangle velocity Shot time Sample No. Material (μm) (°) (m/sec) (min)Invention Al₂O₃ 130 60 60 2.5 sample 1 Invention Al₂O₃ 130 60 60 2.5sample 2 Invention ZrO₂ 140 60 70 3.0 sample 3 Invention Al₂O₃ 120 60 702.0 sample 4 Invention Al₂O₃ 120 60 70 2.0 sample 5 Invention Al₂O₃ 12050 65 1.0 sample 6 Invention Al₂O₃ 120 50 65 1.0 sample 7 InventionAl₂O₃ 100 45 50 1.0 sample 8 Invention Al₂O₃ 100 45 50 1.0 sample 9Invention ZrO₂ 150 70 70 3.0 sample 10 Invention Al₂O₃ 130 45 55 0.5sample 11 Comparative Al₂O₃ 130 60 50 2.5 sample 1 Comparative Al₂O₃ 13060 50 2.5 sample 2 Comparative ZrO₂ 140 60 70 3.0 sample 3 ComparativeZrO₂ 110 70 70 1.5 sample 4 Comparative ZrO₂ 110 70 70 1.5 sample 5Comparative Al₂O₃ 120 50 65 1.0 sample 6 Comparative Al₂O₃ 120 50 65 1.0sample 7 Comparative Al₂O₃ 100 45 50 1.0 sample 8 Comparative Al₂O₃ 10045 50 1.0 sample 9 Comparative Al₂O₃ 130 45 55 0.5 sample 10

As to the obtained samples, an X-ray diffraction measurement by means ofa 2θ/θ focusing optical system with Cu-Kα radiation was performed underthe following conditions: an output: 50 kV, 250 mA; an incident-sidesolar slit: 5°; a divergence longitudinal slit: 2/3°; a divergencelongitudinal limit slit: 5 mm; a scattering slit: 2/3°; alight-receiving side solar slit: 5°; a light-receiving slit: 0.3 mm; aBENT monochromater; a light-receiving monochrome slit: 0.8 mm; asampling width: 0.01°; a scan speed: 4°/min; and a 2θ measurement range:20°-155°. As to the apparatus, an X-ray diffractometer “RINT TTR III”manufactured by Rigaku Corporation was used. The peak intensity of eachplane index of the α-type Al₂O₃ layer was obtained from an X-raydiffraction pattern. A TC (0,0,12) and a TC (0,1,8) were obtained fromthe resulting peak intensity of each plane index. The results are shownin Table 9.

TABLE 9 α-type Al₂O₃ layer Sample No. TC (0, 0, 12) TC (0, 1, 8)Invention 6.2 0.8 sample 1 Invention 7.1 0.8 sample 2 Invention 7.2 1.0sample 3 Invention 7.5 0.5 sample 4 Invention 7.2 0.7 sample 5 Invention5.3 2.4 sample 6 Invention 6.4 1.5 sample 7 Invention 4.1 2.8 sample 8Invention 7.2 1.1 sample 9 Invention 7.3 0.8 sample 10 Invention 8.2 0.5sample 11 Comparative 0.7 0.3 sample 1 Comparative 0.7 1.0 sample 2Comparative 1.2 0.1 sample 3 Comparative 0.6 0.3 sample 4 Comparative0.5 0.4 sample 5 Comparative 4.0 0.3 sample 6 Comparative 0.8 0.2 sample7 Comparative 1.5 1.2 sample 8 Comparative 1.7 0.2 sample 9 Comparative1.0 0.3 sample 10

The residual stress of the α-type Al₂O₃ layer of each of the obtainedsamples was measured by a sin²φ method using an X-ray stress measuringapparatus. The measurement results are shown in Table 10.

TABLE 10 α-type Al₂O₃ layer Residual stress value measured with theselection of a (1, 1, 6) plane Sample No. (MPa) Invention −255 sample 1Invention −260 sample 2 Invention −294 sample 3 Invention −148 sample 4Invention −146 sample 5 Invention 154 sample 6 Invention 152 sample 7Invention 290 sample 8 Invention 286 sample 9 Invention −405 sample 10Invention 50 sample 11 Comparative −234 sample 1 Comparative −230 sample2 Comparative −292 sample 3 Comparative −104 sample 4 Comparative −110sample 5 Comparative 155 sample 6 Comparative 150 sample 7 Comparative284 sample 8 Comparative 296 sample 9 Comparative 48 sample 10

Cutting tests 1 and 2 were conducted using the obtained samples. Cuttingtest 1 is a test for evaluating wear resistance, and cutting test 2 is atest for evaluating fracture resistance. The results of the respectivecutting tests are shown in Table 11.

[Cutting Test 1]

Workpiece material: S45C round bar

Cutting speed: 300 m/min

Feed: 0.30 mm/rev

Depth of cut: 2.0 mm

Coolant: Used

Evaluation items: A time when a sample was fractured, or a when a samplehad a maximum flank wear width of 0.2 mm, was defined as the end of thetool life, and the machining time to reach the end of the tool life wasmeasured.

[Cutting Test 2]

Workpiece material: SCM415 round bar with two equidistant groovesextending in the length direction

Cutting speed: 250 m/min

Feed: 0.40 mm/rev

Depth of cut: 1.5 mm

Coolant: Used

Evaluation items: A time when a sample was fractured was defined as theend of the tool life, and the number of shocks the sample had receiveduntil the end of the tool life was measured. The number of times thesample and the workpiece material were brought into contact with eachother was defined as the number of shocks, and the test was ended whenthe number of contacts reached 20,000 at a maximum. As to each sample,five inserts were prepared and the number of shocks was measured foreach of such inserts, and the average value was obtained from themeasurements of the number of shocks so as to serve as the tool life.

As to the machining time to reach the end of the tool life in the wearresistance test, evaluations were made with grade “A” for 35 minutes ormore, grade “B” for 25 minutes or more and less than 35 minutes, andgrade “C” for less than 25 minutes. Further, as to the number of shocksuntil the end of the tool life in the fracture resistance test,evaluations were made with grade “A” for 15,000 or more, grade “B” for12,000 or more and less than 15,000, and grade “C” for less than 12,000.In such evaluations, “A” refers to excellent, “B” refers to good and “C”refers to inferior, meaning that a sample involving a larger number ofgrade “A”s or “B”s has more excellent cutting performance. The overallevaluation results obtained are shown in Table 11.

TABLE 11 Wear resistance Fracture resistance test test Tool life DamageTool life Sample No. (min) Grade form (shocks) Grade Invention 29 BNormal 18,600 A sample 1 wear Invention 34 B Normal 19,000 A sample 2wear Invention 39 A Normal 20,000 A sample 3 wear Invention 51 A Normal16,400 A sample 4 wear Invention 42 A Normal 18,100 A sample 5 wearInvention 30 B Normal 16,500 A sample 6 wear Invention 39 A Normal14,800 B sample 7 wear Invention 42 A Normal 14,600 B sample 8 wearInvention 29 B Normal 15,100 A sample 9 wear Invention 29 B Normal17,700 A sample 10 wear Invention 27 B Normal 15,500 A sample 11 wearComparative 19 C Normal 12,000 B sample 1 wear Comparative 22 C Normal14,500 B sample 2 wear Comparative 21 C Fracturing 11,300 C sample 3Comparative 14 C Normal 11,600 C sample 4 wear Comparative 21 C Normal10,900 C sample 5 wear Comparative 25 B Fracturing 9,400 C sample 6Comparative 23 C Normal 9,600 C sample 7 wear Comparative 22 C Normal8,200 C sample 8 wear Comparative 21 C Fracturing 5,400 C sample 9Comparative 20 C Normal 10,800 C sample 10 wear

The results of Table 11 show that, as to the evaluations of theinvention samples, each invention sample had grade “A” or “B” in boththe wear resistance test and the fracture resistance test. Meanwhile, asto the evaluations of the comparative samples, each comparative samplehad grade “C” in either the wear resistance test or the fractureresistance test. In particular, each invention sample had grade “A” or“B” in the fracture resistance test, and each comparative sample hadgrade “B” or “C” in such test. Accordingly, it is apparent that thefracture resistance of each invention sample is equal or superior tothat of each comparative sample.

It is apparent from the above results that each invention sample hasexcellent wear resistance and fracture resistance and accordingly has along tool life.

The present application is based on the Japanese patent applicationfiled on Oct. 24, 2016 (JP Appl. 2016-207734), the content of which isincorporated herein by reference.

INDUSTRIAL APPLICABILITY

The coated cutting tool according to the present invention has improvedand excellent fracture resistance without a reduction in wearresistance, whereby the tool life can be extended more than thatinvolved in the prior art, and the coated cutting tool therefore hashigh industrial applicability.

What is claimed is:
 1. A coated cutting tool comprising a substrate anda coating layer formed on a surface of the substrate, wherein: thecoating layer comprises at least one α-type aluminum oxide layer, a TiCNlayer having an average thickness of from 10 μm or more to 20 μm orless, and an intermediate layer comprised of TiCNO; and in the α-typealuminum oxide layer, a texture coefficient TC (0,0,12) of a (0,0,12)plane represented by formula (1) below is from 4.0 or more to 8.4 orless, and a texture coefficient TC (0,1,8) of a (0,1,8) planerepresented by formula (2) below is from 0.5 or more to 3.0 or less.$\begin{matrix}{{{TC}( {0,0,12} )} = {\frac{I( {0,0,12} )}{I_{0}( {0,0,12} )}\{ {\frac{1}{9}{\sum\frac{I( {h,k,l} )}{I_{0}( {h,k,l} )}}} \}^{- 1}}} & (1) \\{{{TC}( {0,1,8} )} = {\frac{I( {0,1,8} )}{I_{0}( {0,1,8} )}\{ {\frac{1}{9}{\sum\frac{I( {h,k,l} )}{I_{0}( {h,k,l} )}}} \}^{- 1}}} & (2)\end{matrix}$ (In formulae (1) and (2), I (h,k,l) denotes a peakintensity for an (h,k,l) plane in X-ray diffraction of the α-typealuminum oxide layer, I₀ (h,k,l) denotes a standard diffractionintensity for an (h,k,l) plane which is indicated on JCPDS Card No.10-0173 for α-type aluminum oxide, and (h,k,l) refers to the ninecrystal planes of (0,1,2), (1,0,4), (1,1,0), (1,1,3), (1,1,6), (0,1,8),(2,1,4), (3,0,0) and (0,0,12)).
 2. The coated cutting tool according toclaim 1, wherein, in the α-type aluminum oxide layer, the texturecoefficient TC (0,0,12) is from 5.0 or more to 8.2 or less.
 3. Thecoated cutting tool according to claim 1, wherein, in the α-typealuminum oxide layer, the texture coefficient TC (0,1,8) is from 1.0 ormore to 2.5 or less.
 4. The coated cutting tool according to claim 1,wherein a residual stress value in a (1,1,6) plane of the α-typealuminum oxide layer is, in at least part thereof, from −300 MPa orhigher to 300 MPa or lower.
 5. The coated cutting tool according toclaim 1, wherein an average thickness of the α-type aluminum oxide layeris from 1.0 μm or more to 15.0 μm or less.
 6. The coated cutting toolaccording to claim 1, wherein an average thickness of the coating layeris from 3.0 μm or more to 30.0 μm or less.
 7. The coated cutting toolaccording to claim 1, wherein the substrate is a cermet or a ceramicbody.
 8. The coated cutting tool according to claim 2, wherein, in theα-type aluminum oxide layer, the texture coefficient TC (0,1,8) is from1.0 or more to 2.5 or less.
 9. The coated cutting tool according toclaim 2, wherein an average thickness of the α-type aluminum oxide layeris from 1.0 μm or more to 15.0 μm or less.
 10. The coated cutting toolaccording to claim 3, wherein an average thickness of the α-typealuminum oxide layer is from 1.0 μm or more to 15.0 μm or less.
 11. Thecoated cutting tool according to claim 2, wherein the coating layercomprises, between the substrate and the α-type aluminum oxide layer, aTi compound layer containing TiN.
 12. The coated cutting tool accordingto claim 3, wherein the coating layer comprises, between the substrateand the α-type aluminum oxide layer, a Ti compound layer containing TiN.13. The coated cutting tool according to claim 5, wherein the coatinglayer comprises, between the substrate and the α-type aluminum oxidelayer, a Ti compound layer containing TiN.
 14. The coated cutting toolaccording to claim 2, wherein an average thickness of the coating layeris from 3.0 μm or more to 30.0 μm or less.
 15. The coated cutting toolaccording to claim 3, wherein an average thickness of the coating layeris from 3.0 μm or more to 30.0 μm or less.
 16. The coated cutting toolaccording to claim 5, wherein an average thickness of the coating layeris from 3.0 μm or more to 30.0 μm or less.
 17. The coated cutting toolaccording to claim 4, wherein an average thickness of the coating layeris from 3.0 μm or more to 30.0 μm or less.